Detector circuit



Jan. 8, 1935. A K. POSTHUMUS 1,986,851

DETECTOR CIRCUIT Filed May 31, 1930 2 Sheets-Sheet l fly)! Y /2 3 1 11 All ammT-m INVENTOR KLAAS FOSTHUMUS BY M.

ATTORNEY Jan.,8, 1935. K. PbsTHuMus 1,986,851

DETECTOR CIRCUIT o Filed May 31, 1930 2 Sheets-Sheet 2 1014 ms'az/i/vcr Va: 21165 N INVENTOR KLAAS POST HUMUS ATTORNEY Patented Jan. 8, 1 935 V Assassi DETECTOR c nema:

' Klaas Posthu'mus, 1 Eindhoven,' "Netherlandmasa i s ignor to Radio Corporationof America, ac ors,

poration of Delaware Application ay,:1,,19a6;*saa1m.458,3 3

The present invention relates to detection of,

more particularlyto r, A i i i p h tude ,of the oscillationson the grid of the dehigh frequency oscillations, the so-called grid detectiom z, y

As is well known, the control electrod e of thei 5 detectoris connected, for grid detection, through a comparatively smallcapacitytothe source. of

the high frequency oscillations, This, as well as the'uni-dir'ecticnal conductivity of the grid-filament path, results in the average potentialofthe grid falling at each high frequency wave, train, owing to the fact that electronsfaccumulate on the grid, the e t ns (being iilmwed leak away through the leakage paths that are presentl on sufficient insulation), orthroughda leakagel re:

fsistance which has been provided, Such fluctu l ations of the average grid potential obviously in-f volve variations of the anode current, which consequently occur in the (audible) rhythm of the wave trains, and canibe observedin the receiver.

being extremely sensitive and" therefore it is almost commonly applied, in contradistinction to anode detection which islpnly of, practical use when the amplitudes of theincominghigh fre- "quency oscillations have'rather' considerable values, or have been raised tosuchvalues." The grid detection described has, however, the drawback,

" tions, the averagegrid potential falls tosuch an extent that, the tube begins towork in the lower bent portion of its characteristic curve, which means that the, average anode currentno longer.-

corresponds to, thevalue, which,as may be read off fromthe staticcharacteristic curve, pertains to the said low grid-potential, but obtains a high er value in consequence ofqthe occurring anodedetection. l

Inthis case, the latter, consequently, counter acts, the grid-detection, breaks the above men tioned proportionality, and, in the case of very strong incoming signals,]it may even tend to in- J verse said proportion thatis to say,rthe recep tion becomes weakerat an increasing amplitude of the received high frequency oscillations. N If, therefore, a, receiving-set adapted for the reception of weak signals and therefore working with grid detection, approaches astrong transmitting station, the peculiar, but undesirable plhe nomenon occurs that this transmitting station Joan only be properly received if the apparatus This method of detectionhas the advantage of is detun ed: either to chefs} to the other side: In,

fact, if the set, is tuned toj resonance, the ampli-i tectorbecornesso large, that l the grid-detection is practically; ntirely, spoiledby the v simultaneously occurring anode det'e'ction. H n m [The invention relates to a circuit arrangementfor grid-detection, in which the abovementioned drawbackis avoided, and whichis based onthe followingnovel principle e If a detector tube does not comprise one, buttwo, ormore, control electrodes, the 1atter.-1 nay beconnectedto an equally large number of points of fa circuit A arrangement in, which highfre-; quency oscillationsfoccur. Intso far as this cone: nection isestablished through agrid condenser i said grids will act, dueto the grid detection, on{

theaverage, anode currentinthe same senseandg independentlv-o f lany possible phase difference between the said points. The question of the phase in which the various-grids are oscillating is,' however, of pi imary importance for the anode arrangement toWhichthegridsare connected, it

, detection which lmay "simultaneously ;occur. By an adequate choice of-the points of the circuit 7 n in is possible tocreate such a phase diiferencebeit tween: these gridsfthatas far as anode detection .is concerned: they willat any instant mutually neutralize their action either entirely or substan-r tially.

vThe simplest case is "that in which there are two control grids between which, a; phase differ- "ence of x? or thereabout is maintained. Ifjin thislcase both grids are lying in one plane, or if, generally speaking, their y amplification factor (or their 4Durchgriif) is the same, the amplir tudes of the high frequency oscillations to be irna pressed upon these grids will at anyinstantghave tube mutually equal inabsol ute value. At different amplification factors a correspondingly different relation-between the oscillation ampli in tudes to be impressed upon the grids must be chosen. In the case ofthree grids they should be, connected to points between which exist phase differences of 120, and so on.

The novel features which I believeto be char acteristic ,of my invention are set forth in par reference tothe following description taken in ticularity inthe appendedclaims, the invention itself, however, as to both its organization and :methodof operation will best be understood by connection with the drawingsin which I have in-,

dicated, diagrammatically several circuit organizations whereby my invention may be carriedinto effect.

by a. series condenser 2 to a tunable input circuit 3 of a high frequency amplifier tube I. ,Thistube comprises a control grid 4,a cathode '5and an anode 6, the latter being-corinectehto onelend of a second tunable circuits-7.- -.Thisl'circuit .com-

prises a variable condenser 8, connected in parallel to a coil 9 which has an. intermediate.tap

ping point 10. ,V v q The end of the circuit 7, which is connected to the anode 6, is also connected by a gridacondenser 11 to agrid .13 ofa detector tube 11, while, the

other end of I the coil 9'- is I connected, through a.

secondgrid condenser 12', to a'second grid 1410f this detector. Furthermore, the tap 10 of the coil.

9 is connected to the;posi ti ve terminal of asource supplying the anode, :current'. fln addition, the

detector tube comprises acathode 15 and an anode 16, the latter being connected by a, telephone 17, or loud speaker, to thesaid positive. t erminal.'

Finally, the twogrids' 13 and 14 are connected to the cathode 15 by leakageresistances 18 -,and,19

respectively.- *f

The operation of the circuit as follower After being amplified by-thetube'I, the'ampli e fied--oscillations-reach thecircuit; 7;, andproduce high frequency voltage variationsiacross the ends of the coil 9,-between which there will be'a phase difference of 180; Assuming that the point 10 lies-in the middle of the coil 9, the'iampli tudes of the oscillations in the'said-en ally equal inabsolute value;

These oscillations are transferred through the condensers 11 and 12 :to the grids 13 "and- 14 re-- ds willbe mutuspectively whose 'average;potentialsyat the passage of a wave train,fall-toaniequal'extent, so 'thatas to the grid detectionthey r'nutu'ally'sup port their operation. On the contrary, thehigh frequency variations, to which 'both gridpote'n v 1 'compensationobtained by the-'use'of inversely working grids, no high frequency'currents at allwill circulate in the anodecircuit of the detector,

so that-it is no longer of any use to couple this circuit back to the grid circuit. In this case, the usual telephone, or by-pass condenserconnected inparallel to the reproducer 17; may also be dispensed with,;since the circulationof highfre quencycurrents in the low frequency'part of the circuit arrangement is already sufliciently prevented on account of-the said-compensation.-- A complete compensation ma'y be approximated as much as possible by arranging the-grids 13 and 14 in one plane and by causing. the rods of these grids to alternate. There is no'objectio'm-however, to arrange the'grids in different-planes provided this arrangement is taken into account when selecting the position ofthe-point--10. -A

drawback of e the circuit arrangement according to Fig. 1 consists in that both electrodes-of the It should be observed that in case of an'ideal variable condenser 8 oscillate, owing to which the so-called hand effect might cause trouble.

In order to avoid this, the arrangement may be such as is represented in Fig. 2 which diifers from Fig. 1 only as to the, circuit 7, for in Fig. 2 the condenser 8 is not inserted between both ends of the coil 9, but between the anode end of this coilyand the pointxlO which does not oscillate, the tuning of the circuit? beingthus 'siniplified.

Fig. 3 shows two curves (a) and (b) which repi'resent the low frequency alternating tension in .yolts occurring at the reproducer 17, as a function of the amplitude of the high frequency grid os- ;;..cillationsrinvolts, ,viz,.for normal grid detection and for multiplecompensated grid detection, accordingto the invention, respectively.

For. plotting the curve (19) use has been made of a detector tube comprising two grids lying in one plane and provided each with a grid condensers-The advantage obtained by the invention clearly appears from.this graph. At low values, of the high frequency grid oscillations, up

to about-l voltythedifference between both methods of detection is only slight, but even at 3 volts new method becomes manifest; j

It consequently appears that the high frequency load of the detector can be considerably raised,

advantage in the neighborhood of strong transmitting stations, and which, in addition will alwhich,as mentioned at the outset, affords a greatvv frequency amplifiervalve of rather-high power directly-behindthe detector and of applying nev-. j

ertheless the full load to this valve, may be con-.

sidered a general advantage.

For'the principle of the invention it is imma-w terialwhether thedetector is preceded by one,.two'

or more high frequency amplification stages or is fed directly from-theaeriaL, Besides, it is not necessaryto connect all the-grids of the .detector valve to a grid condenser, though it is advisable todo so in view of the sensitiveness and of the,

symmetry desirable-for the. compensation of the T anode detection;

It is to be understood that the expression elec,-,

j tron path which occurs in certain'of the follow- :1 ing claims, refers'to the electron stream, or path, which existsbetween the cathodeandanode in the absence-of grids. This termis not intended to take'into account any eifect of the gridsin (breaking up the'electron path'into smallerpaths.

While I, have indicated and described several isystemsfor carrying my invention into effect, it

departing-from the scope of my invention as set j forth in the appended claims.

What I claim is: I 1. A detector circuit arrangement comprising a detector tube of the type including only a single anode and atleasttwogrids-arrangedfor grid circuit rectification, an input circuit including an oscillating end of the coil-,- an intermediate non.-

oscillating point of the coilbeingconnected by ,a uning condenser to one ofthe said-oscillatingen'clsm tube provided-with a cathode; a single "anode; and

--at least two grids-disposed in the sameelectron inductance coil,'each grid being connected to an 2. A method of operating an electron-discharge ergy of relatively high intensity, which consists in collecting said signal ,energy, amplifying the qprectification.

capacity, and saidcathode.

collected energy to said intensity, impressing the amplified energy upon one of the grids, and simultaneously impressing a radio frequency voltage of signal frequency on the other; grid of such a magnitude and phaseas to substantially neutralize the effector the signal frequency ,variation onthe said electron path. V l 3. A method of operating an electron, discharge tube, provided with a cathode, anode, and at least two grids disposed in the same electron path betweenthe cathode and anode and arranged for grid rectification, each grid afiectingsubstan tially theentire electron path, which consists in impressing signal modulatedradiofrequency en ergy of relatively high intensity upon a grid of the tube, simultaneously impress'ing'similar en ergy upon the other. grid, and adjusting the phase of the energy applied to the second grid so 'asto substantially neutralize the effect of the signal frequency variation on said electron path. l

4. A method of operating an electron discharge tube, provided witha cathode, anode, and at least two grids disposed in the same electron pathbetween the cathode and anode and arranged for grid rectification, each grid affecting ,substan tially the entire electronpath, whichl consistsin impressing signal modulated radio frequency energy of relatively high intensity .upon a grid oi the tube; simultaneously impressing similar energy upon the other grid, and adjusting thephase of, the energy applied tothe second grid so as to substantially neutralize the effect of the signal frequency-variation. on said electron path and 1 directly employingthe anode current of the tube for rendering said signals audible. i 5. A detector circuit comprising an electron discharge tube including a singleanode, a cathode and at least two grids, said tube being provided *ywith a resonant ,input circuit including an inductance coil, the grids being connected to oppositeends of said coil,,said grids being co-planarly arranged,,and means in at least one of said grid circuits to permit said 6. In combination, a source a pair of grids and a cathode and being provided giwith a resonant input circuit including an in ductance coil, said grids being co-planarly arranged, means for connecting a grid of the tube to one end ofsaid coil, said connectingmeans ineluding a capacity, and additional means including a capacitybetween the otherend of said coil and the other grid,for substantially diminishing the radio frequency component of anode current in the output circuit of said tube, and a resistor connected from each grid, adjacent its said 7; The method of operating adetector tube,

which tube has a pair of grids arranged for grid rectification and disposed in the same electron stream between the cathode and anode of the tube, each grid affectingsubstantially the entire electron stream, with a substantially linear charfrequency input voltages, which method includes the step of impressing in phase opposition upon circuit to detect by grid of desired radio frequency signals, a detector circuit comprising 3 an electron discharge tube having a single anode,

said grids signal energyto be rectified, and con-s rent of the tube in such amanner that the radio frequency component of anode current is greatly reduced.

8. In combination, in a detectorstageoa tube trolling the effect of said grids on the; space cur--v provided with a cathode,a single anode, asingle electron stream between said cathode and anode,

and a pair of controlgrids disposedin thesaid electron stream, each grid affecting substantially the entire electron path,.a resonant signal input circuit includinga coil, said gridsbeingconnect ed to the opposite ends of said coil whereby .'signa l energy is impressed on said grids with a=phase difference of 1180 degrees, .a connection between an intermediate point of said coil and a point the cathode to plate circuit of ,said tube, saidgrids being so relatively arrangedthatthey have:sub-

lnfcombinationyin a detector stage, a tube provided with a cathode, a single-anode, andia pair of cO-planar control grids,:aresonant signal; input circuit including a coil, said grids being connected to the opposite ends of said coil whereby signal energy is impressed on said grids with a phase difference of 180 degrees,ea connection be,-

tween an intermediate pointof said coil and'a point-in the cathode towplate circuit ofv saiditube, andgrid circuit rectification means connected to each grid.

.10. In combination, in a detector stage, 'a tube provided with a cathode, a single anode, and a pair of co-planar control grids, a resonant signal input circuit including a coil, said grids being connected to the'opposite endsiof said coil whereby circuit rectification means connected to each grid. 11. In combination, in a detector stage, a tube provided with a cathode, asingle anode, and a pair of co planar control grids,a resonant signal input circuit including a coil, said grids being connected to the opposite ends of said coil where-.

by signal (energy is impressed on said: gridswith: a phase difference of 180 degrees, a connection between an intermediate point of said coil and a point in the cathode to plate circuit of said tube; grid circuit rectification means connected to at least one grid, and at least one stageof signal energy amplification connected-to said resonant input circuit.

12. In combination, in a detector stage, a tube provided with a cathode, a single anode, a'nda pair of control grids, a resonant signal input 'circuit including a coil, said grids beingconnected to the opposite ends of said coil whereby signal energy is impressed on said grids with a phase difierence of 180 degrees, a connection between,

an intermediate point of said coil and a point in the cathode to plate circuit of said tube, grid circuit rectification means connected to each grid anda variable tuning condenser connected between the said intermediate point of said coil and the high potential end of the coil.

13. A method of employing an electron discharge tube, provided with, a cathode electrode, a single anode electrode, anda grid electrode and at least one auxiliary electrode, both disposed in the same space current path between the cathode and anode, said grid and auxiliary electrodes each affecting substantially the entire space cur- 

